1. Field of the Invention
The present invention relates to a process for the preparation of a methacrylimide group-containing polymer having an excellent heat resistance, transparency and moldability.
2. Description of the Related Art
A methacrylic polymer resin containing a methacrylimide group (hereinafter referred to as "methacrylimide group-containing polymer") is a thermo-plastic polymer resin having a high heat distortion temperature and a high transparency, as is well-known (see Japanese Examined Patent Publication No. 60-38,404 and Japanese Unexamined Patent Publication No. 59-31,012).
However, a methacrylimide group-containing polymer obtained by heat-treating a methyl methacrylate polymer in the presence of an agent capable of forming a methacrylimide ring structural unit, such as a primary amine, has a poor moldability, though the polymer retains a high heat distorsion temperature and a high transparency. The term "moldability" used in the instant specification means particularly, the processability at the injection molding conducted at a high temperature, especially a temperature of 300.degree. C. or more. The above-mentioned conventional methacrylimide group-containing polymer has a problem in that if the temperature is not lower than 300.degree. C. at the melt injection molding, blowing is caused or silver streaks appear in the obtained molded article, and therefore, the polymer has a poor moldability.
As the means for improving the moldability of the methacrylimide group-containing polymer, there has been tried a method in which the polymerization degree of the polymer is reduced and molding is carried out at a lower temperature.
In this method, however, since the polymerization degree of the methacrylimide group-containing polymer is reduced, reduction of the mechanical strength of the obtained molded article cannot be avoided.